Hello,
A few days ago I had this message on my system as well.
The following command then helped:
sudo pacman-key --refresh-keys
(Took a long time to go through.)
But now the problem seems to be:
The currently downloadable ISO (KDE/Plasma) can no longer be installed online. Only the offline installation still works.
The online installation aborts with an error message.
Unfortunately, I don’t have this error message here because I didn’t know how I could have copied it out of the “live environment”.
But I was asked if I would like to email the error message, which I said yes.
Whether or what has arrived, I do not know.
But the error message had something to do with updates that could not be performed! And I suspect that it is precisely the problem described in the thread title.
Another indication of this is that updates also do not work after offline installation, and the error message mentioned above appears.
After
sudo pacman-key –refresh-keys
does it work then.